Exhaust systems in modern cars are provided with mufflers comprising a shell which is internally lined with a noise-deadening material, typically rock wool. The exhaust gas in the shell is piped into an insulated chamber, sometimes known as “reflection chamber”, via a first pipe, and then to one/more intermediate pipes joined to the exhaust pipes. Since turbulences and counter-pressures inside the insulated chamber considerably affect the power performance of the engine, it is also known to convey the gas flow within the insulated chamber via a connecting box having perforations over its entire surface and provided with two side holes for connection to respective exhaust pipes.
Although the above arrangement is satisfactory as far as noise-deadening is concerned, however it is not satisfactory in terms of performance of the engine, because the profile of the perforated box hinders the optimal flow of the exhaust gas.